Abstract:
Modern aerospace gas turbines require
large numbers of small diameter holes ( < 1 mm ) to provide
cooling in the turbine blades, nozzle guide vanes, combustion
chambers and afterburner. A typical modern engine will
have ~ 100,000 such holes. Drilling these cooling holes
by Nd-YAG laser is now well established. Such holes can
be successfully produced by laser trepanning, but this
is a relatively slow process compared with laser percussion
drilling both drilling techniques are performed using
direct free space mirror delivery system. The aerospace
industry would like to move to a fibre optic delivery
system, but the only fibres capable of carrying the high
peak powers involved are 600 Ám core fibres with the associated
poor beam and poor hole quality. By reducing the peak
power of the laser and careful control of laser pulse
and drilling parameters useful hole with good hole quality
can be achieved. This paper investigates these parameters
using a GSI Lumonics new JK700 series laser with a 400
Ám optical fibre delivery system.